1. Field of the Invention
The present invention relates to the manufacture of articles using solder, particularly the manufacture of articles having electrical connections which use solder to provide areas where electrical contacts are attached or electrical connections made, and most particularly to the manufacture of circuit boards where solder is used to provide electrical contact points or points of adhesion for electrical connections, and to the removal of excess solder in such manufacturing processes.
2. Background of the Art
Solder has been used for literally centuries in the adherence of metal components together. Solder is a relatively low melting metal or alloy (usually lead and tin, with other optional ingredients therein) which is melted between two components which are intended to be adhered. Because the solder usually melts at a temperature below the melting point of the metals which are to be adhered together, the solder will bond the two surfaces (the primary materials) to be adhered without the need of using temperatures which could melt or damage the primary materials, as would be the case in welding. Soldering is generally performed by cleaning two primary surfaces, applying a flux (which may further clean or maintain the cleanliness of the surface) which enables or enhances the surface to be wetted by the solder. After the surfaces have been cleaned and a flux applied, the solder is heated, allowed to flow between the two surfaces, and then cooled. The cooled solder forms a solid bond between the two primary surfaces.
One of the desirable aspects of soldering in the electrical and electronic arts is the fact that the bond between the two primary surfaces is conductive. This allows the use of the soldering technique between electrically transmissive elements, and in fact enables electrical connections to be readily effected between electrical elements. Solder deposits are often used in the electrical/electronic (the terms may be used alternatively or collectively for the description of the present invention) industry to provide connection points in premade circuit boards. The board or circuit is constructed with the electrical/electronic configuration built into the board, and the specific points where other electrical connections are to be made to the board are provided with solder points so that a connecting component may be aligned with the circuit board, and the connecting component may be heated in aligned contact (the electrical connectors aligned with the solder points where they are to be bonded) with the circuit board and the components and circuit heated to bond the components to the circuit board through the solder points.
In the manufacture of circuit boards having large numbers of point-to-point contacts needed between components, the detail in the electronic/electrical configurations and the solder points can be very complex and require great precision in the location and volumes of solder on the circuit board. These complex arrangements of electrical/electronic connections can be prepared by a number of different methods. The individual contact points may be manually applied or the entire distribution of solder points may be applied by printing type process (screen application, gravure coating, etc.). In either case, mistakes in the positioning or quantity of solder applied may occur. These mistakes, usually in the form of excess or misaligned solder deposits, can adversely affect the performance of the circuit board by preventing proper alignment of the board or a chip on the board (because of a physical anomaly in the presence of a bump or mis-positioning of solder), or the absence of solder preventing a proper electrical connection to be accomplished. Because of the desire to reduce manufacturing waste, both because of environmental concerns and the expense involved in waste, it is desirable to recover and salvage any mistakenly configured circuitry so that the circuit board may be reused. Many different types of efforts have been attempted to provide materials and processes for recovering misconfigured circuit boards.
There are basically three types of processes which are used to control or remove solder from circuit board applications. One type of process levels solder which remains on a circuit board. This leveling may be accomplished with any one of or combination of liquid (solvent) application, thermal softening, and air knifes. Such processes are exemplified as system patents by U.S. Pat. Nos. 5,593,499; 4,614,858; 4,412,641; and U.S. Pat. No. 4,285,091. Another process involves solvent or carrier material to the surface. This is shown in some of the system patents described above and are shown with fluidized beds and/or solvents in U.S. Pat. Nos. 4,769,083; 3,924,794; and 3,865,298. Wicking materials, usually applied only to the specific solder joints or collection of solder connections for an individual component are shown, for example, in U.S. Pat. Nos. 4,323,631; 4,923,521; 5,065,931; 3,715,797; 4,416,408; 4,934,582; and RE 32,806.
U.S. Pat. No. 4,934,582 describes a method and apparatus for the removal of solder mounted surface mount electronic components which includes the removal of old solder, broken leads, and the electronic component without damaging other devices on the substrate. A desoldering braid is shaped to cover each of the electronic component's outer lead bonds without contacting the component's base. The desoldering braid is heated and brought in contact with the bonds until the solder flows into the desoldering braid and any broken outer leads attach to the desoldering braid. Upon removal of the desoldering braid the electronic component can be lifted off the surface. The desoldered solder joints will contain a thin uniform coating of solder less than approximately 50 micro inches thick. This allows for removal and replacement of solder mounted electronic components with leads on center lines spaced less than 0.020 inches.
U.S. Pat. No. 4,905,371 describes an apparatus and method for a cleaning process control. The apparatus includes a printed wire circuit board that is made on a Pyrex glass or other transparent substrate. Components are attached to the printed wire circuit board and then the circuit card assembly which is formed is cleaned using a selected cleaning process. The circuit card assembly can then be inspected to determine the effectiveness of a particular cleaning process by flipping over the transparent circuit card, peering through the substrate to inspect for corrosion and solder balls. The circuit card assembly can then be cleaned more extensively and used again to check a different cleaning process.
U.S. Pat. No. 4,416,408 describes a solder removing device for absorbing solder which has been rendered molten by the application of heat, including an open-mesh structure comprising a strand and formed by knitting, as a primary example, at least the surface of the strand being metallic and receptive to solder flux (and indeed being coated with solder flux rendering it more capable of wetting with molten solder). The open-mesh structure enables the device to absorb solder more freely and in greater quantities than can prior braided devices in which the multiple strands are contiguous.
U.S. Pat. No. 3,724,418 describes the application of a thin uniform coat of hot tin lead solder to the exposed copper circuitry of electrical circuit boards utilizing a fluxing station, a standing wave soldering station, a hot liquid spray leveling station, a hot water spray cleaning station, a high volume air spray drying station and a conveyor for transporting the electrical circuit boards past the aforementioned stations. The apparatus contains those pumps, motors, tanks, and electrical and hydraulic systems necessary to support the aforementioned stations.
U.S. Pat. No. 3,715,797 describes a rope-like member of braided heat conducting metallic wires coated with a second metal and a flux is applied to a solid solder joint. Heat applied to the rope-like member liquefies the solder which in turn is absorbed into the member thereby removing solder from the joint.
U.S. Pat. No. 5,593,499 describes a dual air knife assembly for removing excess solder and leveling any remaining solder on a passing circuit board with a gas from a gas source includes a first and second air knife. The first air knife has a first passage with a first inlet adapted to connect to the gas source and a first outlet adapted to be positioned adjacent the passing circuit board. The second air knife has a second passage with a second inlet connected to the gas source and a second outlet adapted to be positioned adjacent the passing circuit board. The first air knife is adapted to be positioned substantially perpendicular to the circuit board and the second air knife is adapted to be positioned at an angle less than 90 degrees and preferably between 20 and 60 degrees to the circuit board. The dual air knife assembly may include a spacer which separates the a first and second air knife and is recessed from the outlets of the a first and second air knife to create an expansion chamber. The distance the first and second outlets are from the passing circuit board and the temperature and pressure of the gas exiting from the a first and second air knife should all be substantially the same. Typically, the dual air knife assembly is used in a soldering system which includes a conveyor, a flux station, and a solder station. The dual air knife assembly is used in a process referred to as "hot air solder leveling" to remove excess solder and more evenly distribute any remaining solder. A pair of dual air knife assemblies may be used in another soldering system where excess solder is removed and any remaining solder is leveled on both sides of a circuit board.
U.S. Pat. No. 5,065,931 U.S. patent No. describes a process for repairing electronic device packages, the problem of removing solder remnants on substrate bonding pads is solved by, first etching a pattern in silicon and metallizing the pattern to make a silicon wick. The solder remnants on the bonding pads are melted, and the etched pattern of the silicon wick is brought into contact with the remnants to remove them by capillary action. It is often convenient to heat the silicon wick so that solder remnants melt when the wick is brought into contact with them.
U.S. Pat. No. 5,007,574 describes a desoldering tool which has a removable cartridge and a base unit having an assembly interior including a solder collection chamber and a removable vacuum source for developing a vacuum in the bottom of the chamber under a removable porous solder retention pad, the cartridge having a temperature self-regulating heater therein and a tail pipe extending from a tip of the cartridge to a position above the solder collection chamber, and a vacuum seal between the cartridge and the base unit to maintain the vacuum and reduce transfer of heat from the tip.
U.S. Pat. No. 4,923,521 describes a process for repairing electronic device packages. The problem of removing solder remnants on substrate bonding pads is solved by, first, etching a pattern in silicon and metallizing the pattern to make a silicon wick. The solder remnants on the bonding pads are melted, and the etched pattern of the silicon wick is brought into contact with the remnants to remove them by capillary action. It is often convenient to heat the silicon wick so that solder remnants melt when the wick is brought into contact with them.
U.S. Pat. No. 4,614,858 describes a desoldering tool for removing soldered electronic components from printed circuit boards which includes a plurality of electric heater bars disposed in spaced apart, opposed relationship so as to grasp the component to be removed. The heater bars are shaped to contact the solder terminations to be desoldered and are composed of an alloy of high electrical resistivity, such as Nichrome. The heater bars are each removably attached to a pair of cantilever spring plates carried by the enlarged end of the handle of the desoldering tool by a different pair of bus bars enclosed in a molded plastic housing providing support and electrical insulation. One bus bar of each pair is rigidly attached to one spring plate while the other bus bar is attached to the other spring plate so that the cantilever spring plates urge the heater bars against the solder terminations and retain the component for physical removal. The leads of a power cord extending through the handle are electrically connected to the spring plates for supplying heating current to the heater bars through the bus bars.
U.S. Pat. No. 4,412,641 describes a device for desoldering electronic components from circuit boards which has a soldering nozzle which produces a solder wave that is directed from below the circuit board against the component to be desoldered; thereby dissolving previous solder bonds. The component can then be lifted out from above and suction is applied from below to the now-opened bores of the circuit board, to remove residual solder from them. A new component can then be installed, using the same equipment.
U.S. Pat. No. 4,323,631 describes a solder removing device is disclosed including fibers of temperature-resistant non-metallic material, such as a synthetic polymeric material, for example FEP or PTFE, which are coated with a metal rendering them more receptive to solder flux. The metallized fibers are coated with solder flux rendering them more capable of wetting with molten solder, interstices between the fibers serving to absorb molten solder by capillary attraction.
U.S. Pat. No. 4,285,091 and U.S. Pat. No. 4,187,973 describe a desoldering system which operates in conjunction with a soldering instrument which may be of the temperature controlled type disclosed and specifically designed for simultaneously desoldering dual-in-line integrated circuit packages, having for example 14 or 16 pins, multiple pins for transistors, 8 or 10 pin round integrated circuit packages and the like. Due to the large throughput of air required to the vacuum system the desoldering attachment features large inlet pipes. The desoldering tip is directly screwed onto the heating element of a soldering instrument surrounded by an air tight sleeve which includes a filter or trap for the solder. The sleeve of the desoldering instrument in turn is connected to another barrel which may include an additional filter and is provided with a three-way trigger valve. The valve selectively connects the desoldering attachment to a vacuum line to pull in the solder, it closes the vacuum line when not depressed, and provides access to the outside air for removing the solder collected in the desoldering attachment. A solder extractor is provided for this purpose. It is connected to a vacuum line and features a snap action to uncover a vacuum connection whereby the desoldering tip and its sleeve may be cleaned by sucking out the solder.